1. Field of the Invention
The present invention relates to a liquid crystal display device, and more particularly, to a technique effectively applied to a liquid crystal display device that is used as a display of a portable electronic device.
2. Description of the Related Art
Liquid crystal display devices are one of devices that have conventionally been used as a display of a portable electronic device such as a cellular phone and a personal digital assistant (PDA).
Liquid crystal display devices are display devices that have a liquid crystal display panel in which a liquid crystal is sealed between a first substrate and a second substrate. The components of the liquid crystal display panel are arranged such that the liquid crystal and the second substrate are nearer to a viewer (person viewing the display panel) than the first substrate.
In a general liquid crystal display device, the first substrate is an insulating substrate, for example, a glass substrate. Scanning signal lines, video signal lines, TFT elements, pixel electrodes, an orientation film, and others are formed on a surface of the first substrate, which is why the first substrate is often called a TFT substrate. The second substrate is an insulating substrate, for example, a glass substrate, and is often called an opposite substrate. Formed on a surface of the second substrate are a light-shielding layer, which divides a display area into pixels, a color filter, an orientation film, and others. Opposite electrodes, which are provided to drive the liquid crystal together with the pixel electrodes, are formed on the opposite substrate side in some cases, and on the TFT substrate side in other cases.
Recent portable electronic devices are ever becoming thinner and lighter, prompting liquid crystal display devices (liquid crystal display panels) and other displays for portable electronic devices to be thinner. One way to obtain a thinner liquid crystal display panel is to reduce the thickness of the insulating substrate (glass substrate) in one or both of the TFT substrate and the opposite substrate.
Another way to obtain a thinner liquid crystal display panel has lately been proposed in which one or both of the TFT substrate and the opposite substrate employ plastic substrates (resin substrates) as insulting substrates instead of glass substrates (see, for example, JP 08-006039 A).
Conventionally, a liquid crystal display device used in a cellular phone or other portable electronic devices is often built inside a casing (exterior parts) of the portable electronic device which has an opening in a portion corresponding to a display area of the liquid crystal display panel. The opening in the casing is, in most cases, covered with a protective cover made of acrylic resin or the like in order to protect the liquid crystal display panel. This structure is beginning to make further thickness reduction of the display part of a cellular phone difficult, and has problems such as lowered visibility of displayed video or images due to a layer of air between the liquid crystal display panel and the protective cover.
A solution for making it possible to further reduce the thickness of a liquid crystal display device for cellular phones and the like while preventing the visibility of displayed images or the like from dropping has been proposed in which a resin plate functioning as the protective cover is attached to a face of the liquid crystal display panel that faces the viewer. The resin plate is attached to the liquid crystal display panel, by attaching the resin plate to a polarization plate that is nearer to the viewer than the opposite substrate (second substrate) with, for example, an adhesive or bonding material so that the resin plate and the polarization plate are in close contact with each other.
Attaching the resin plate to the polarization plate with an adhesive or bonding material has a problem in that, if the adhesive or bonding material is the same acrylic resin-based adhesive or bonding material that is used to attach an upper polarization plate to an insulating substrate (glass substrate) constituting the opposite substrate, the adhesion of the adhesive or bonding material to the resin plate is weak and the resin plate becomes easily detached.